1. Field of the Invention
The present invention relates to a device for measuring three dimensional shape.
2. Background Art
Generally, when electronic components are mounted on a printed board, firstly, cream solder is printed at certain positions on the electrode pattern. Thereafter, the electronic components are temporarily fixed to the printed board by use of viscosity of the cream solder. Thereafter, the aforementioned printed board is conveyed to a reflow furnace, the printed board is subjected to a certain reflow step, and soldering is performed. In recent years, inspection of the printed state of the cream solder has been required at a stage prior the printed board being conveyed to the reflow furnace. A device for measuring three dimensional shape is used during this inspection.
In recent years, there have been proposals for various types of devices for measuring three dimensional shape by the use of light (so-called contact-free devices for measuring three dimensional shape), such as technology relating to devices for measuring three dimensional shape using the phase shift method.
A device for measuring three dimensional shape using this phase shift method uses an irradiation unit composed of a light source and a sinusoidal wave pattern filter and irradiates a light pattern having a sinusoidal wave-shaped (i.e., stripe shaped) light intensity distribution upon an object being measured (i.e., printed board in this case). Then, a point on the board is observed using an imaging unit disposed directly above the board. A CCD camera or the like composed of a lens, and imaging element, or the like is used as the imaging unit. In this case, the intensity I of light at a point P on the image plane is given by the below listed formula:I=e+f×cos φ
(within the formula, e=non-modulated light noise (offset component), f=sine wave contrast (reflectivity), and φ=phase imparted by roughness of the object).
During irradiation, the light pattern is moved, and the phase is changed, for example, in 4 stages as φ+1, φ+π/2, φ+π, and φ+3π/2. Images of the corresponding intensity distributions (I0, I1, I2, and I3, respectively) are read, and the modulated component a is found based on the below listed formula.α=arctan {(I3−I1)/(I0−I2)}
Using this modulated component, the three dimensional coordinates (X, Y, Z) of the point P on the object to be measured, such as a cream solder or the like, are found, and these coordinates are used to measure three dimensional shape (particularly height) of the object to be measured.
However, the actual object to be measured may include both high points and low points. In the case of a cream solder, for example, although there are thin film-like creams solders, there are also protruding cream solders that assume a circular truncated cone shape. When the gap between lines of the irradiated light pattern is widened in concert with the maximum height among such objects to be measured, resolution ability becomes poor, and precision of the measurement may worsen. On the other hand, although it is possible to attempt to improve precision by narrowing the gap between the lines, this may result an insufficient range of height capable of measurement (e.g., due to change of the fringe orders).
Therefore, technology has been proposed that combines light patterns having different pitches (i.e., by combining a light pattern having a short pitch and a light pattern having a long pitch, see Patent Document 1). In this manner, it is possible to prevent loss of resolution in the height direction, and it is possible to widen the height range that is capable of measurement.